1. Field of the Invention
The invention relates to a length-adjustable piston cylinder unit and to a safety device of a piston cylinder unit of this type.
2. Background Art
A large number of length-adjustable piston cylinder units of this type are known which comprise a casing filled with a fluid and which are operable from outside. These piston cylinder units are for example used for angle adjustment of a backrest of a seat such as a passenger seat for an aircraft. By actuating a release lever or a release button at the seat, an operator is able to randomly select and adjust the angle of the backrest within a defined angular range. A drawback is that when the piston cylinder unit fails, for example in the event of an accidental escape of the fluid from the casing, the piston cylinder unit is no longer operable, and consequently, no longer adjustable.
In the example of the passenger seat in an aircraft, the failure of the piston cylinder unit may become noticeable for example when the backrest to be adjusted using the piston cylinder unit drops into a horizontal position without being damped. In this case, passengers are on the one hand no longer allowed to use the seat for safety reasons; on the other hand, they cannot be expected to use the seat for reasons of comfort. Moreover, the vibrations occurring in the normal operation of the aircraft may cause disturbing rattling noises in the pressure-relieved, in other words pressure-less piston cylinder unit.